The Threat of Global Warming causing Near-Term Human Extinction

The image below, from an earlier post, shows that temperatures typically moved up and down by roughly 10°C (ten degrees Celsius, or eighteen degrees Fahrenheit, i.e. 18°F) between a glacial and interglacial phase of the ice ages, suggesting that a 100 ppm rise of carbon dioxide and 300 ppb rise of methane go hand in hand with a 10°C temperature rise. In other words, it looks like high levels of greenhouse gases in the atmosphere have already locked us in for a future temperature rise of 10°C.

How fast could temperatures rise?How fast could such a rise eventuate? There a number of reasons why - despite the high levels of greenhouse gases in the atmosphere - a huge temperature rise has until now unfolded only slowly, including:

Carbon dioxide emissions reach their greatest warming impact ten years after release. In other words, the full wrath of the carbon dioxide emitted over the past decade is yet to come.

A rapid temperature rise is held off by the temporary masking effect of aerosols emitted when burning fuel (especially sulfur dioxide from coal-fired power plants). Once this masking effect falls away, a huge sudden rise in temperature can be expected.

A rapid temperature rise is further held off by the fact that some feedbacks can take time to kick in. There is a huge (but decreasing) capacity of oceans, ice sheets and glaciers to act as a buffer for heat. Demise of the ice and snow cover in the Arctic and methane releases from the seabed of the Arctic Ocean can take time to eventuate and much sunlight is still reflected back into space by the snow and ice cover in the Arctic. However, even though their impact may now look only minimal, one or more feedbacks can cause a dramatic non-linear rise, speeding up the way one or more feedbacks kick in, not only in terms of progression of a non-linear rise, but also due to interaction between feedbacks.

As an example of a non-linear temperature rise, Arctic sea ice demise is causing more heat to be absorbed in the Arctic, resulting in further decline of the snow and ice cover, in turn causing more sunlight to be absorbed (rather than reflected back into space as before). This self-reinforcing feedback loop accelerates warming in the Arctic.

Much carbon is stored in large and vulnerable pools (see image below) that have until now been kept stable by low temperatures. A rapid temperature rise would hit vulnerable carbon pools hard, making them release huge amounts of greenhouse gases, further contributing to the acceleration of the temperature rise.

The scenario of a rapid 10°C temperature rise thus becomes a distinct possibility when considering the size and vulnerability of some of the terrestrial and marine carbon pools and the combined warming impact of:

Falling away of the masking effect that aerosols currently exercise over global warming; and

Feedbacks causing even higher levels of greenhouse gases (carbon dioxide, methane, water vapor, ozone, etc.), resulting in less heat being radiated from Earth, while increasingly less sunlight is getting reflected back into space (albedo decline).

The Potential For Huge Methane Releases

The methane feedback deserves some further attention. Note that the above Unesco image gives an estimate of 10x10³ or 10,000 Gt C for ocean methane hydrates, but that several studies give even higher estimates, as illustrated by the image below, from Pinero et al.

The amount of carbon stored in hydrates globally was in 1992 estimated to be 10,000 Gt (USGS), while a later source gives a figure of 63,400 Gt C for the Klauda & Sandler (2005) estimate of marine hydrates.

Methane hydrates are present at many locations. Further warming of the Gulf Stream is causing methane eruptions off the North American coast. Methane eruptions from marine sediments have also been reported off the coast of New Zealand and in many further locations.

Methane hydrates in marine sediments aren't the only type of hydrates that should be considered. Methane also appears to be erupting from hydrates on land in Siberia, on Antarctica, on the Qinghai-Tibetan Plateau and on Greenland. The hydrates are kept stable by the pressure of large volumes of snow and ice, but wild weather swings could cause cracks and the resulting pressure changes could destabilize such hydrates. Methane is also present in large quantities in lakes, such as at the bottom of Lake Baikal.

Furthermore, methane contained in hydrates isn't the only type of methane that is contained in marine sediments. Marine sediments also contain methane in the form of free gas and carbon that could be transformed by microbes into methane.

Methane and carbon contained in marine sediments typically have an organic origin. Additionally, there is mantel methane, which has a geological origin and can rise through the sediment in the form of free gas or can form hydrates in marine sediments.

The sheer size of the above carbon pools makes that there is a huge danger that methane levels in the atmosphere will grow rapidly, due to releases from methane hydrates and from terrestrial permafrost. What adds to the danger of such methane releases is that levels of greenhouse gasses in the atmosphere currently are very high and rising rapidly.

How fast could such a temperature rise eventuate? As above image also shows, such a rise could take place within a few years. The polynomial trend is based on NASA January 2012-February 2017 anomalies from 1951-1980, adjusted by +0.59°C to cater for the rise from 1750 to 1951-1980. The trend points at a 3°C rise in the course of 2018, which would be devastating. Moreover, the rise doesn't stop there and the trend points at a 10°C rise as early as the year 2021.

The bottom part of the above image shows the warming elements that add up to the 10°C (18°F) temperature rise. Figures for five elements may be overestimated (as indicated by the ⇦ symbol) or underestimated (⇨ symbol), while figures in two elements could be either under- or overestimated depending on developments in other elements. Interaction between warming elements is included, i.e. where applicable, figures on the image include interaction based on initial figures and subsequently apportioned over the relevant elements.

A closer look at each of these warming elements further explains why abrupt warming could take place in a matter of years. As far as the first two elements are concerned, i.e. the rise from 1900 and the rise from 1750 to 1900, this has already eventuated. The speed at which further warming elements can strike is depicted in the image below, i.e. the rise could for a large part occur within years and in some cases within days and even immediately.

Assessing the Danger

The danger can be looked at on three dimensions: timescale, probability and severity. On the severity dimension, a 10°C temperature rise is beyond catastrophic, i.e. we're talking about extinction of species at massive scale, including humans. On the probability dimension, the danger appears to be progressing inevitably toward certainty if no comprehensive and effective action is taken.

In terms of timescale, a 10°C temperature rise could eventuate within a matter of years, which makes the danger imminent, adding further weight to the need to start taking comprehensive and effective action, as described in the Climate Plan.

The Threat

With little or no action taken on global warming, it appears that the Antropocene will lead to extinction of the very human beings after which the era is named, with the Anthropocene possibly running from 1950 to 2021, i.e. a mere 71 years and much too short to constitute an era. In that case a better name for the period would be the Sixth Extiction Event, as also illustrated by the image below.

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The Climate Plan calls for comprehensive action through multiple lines of action implemented across the world and in parallel, through effective policies such as local feebates. The Climate Plan calls for a global commitment to act, combined with implementation that is preferably local. In other words, while the Climate Plan calls for a global commitment to take comprehensive and effective action to reduce the danger of catastrophic climate change, and while it recommends specific policies and approaches how best to achieve this, it invites local communities to decide what each works best for them, provided they do indeed make the progress necessary to reach agreed targets. This makes that the Climate Plan optimizes flexibility for local communities and optimizes local job and investment opportunities.

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Global temperatures are rising fast. In the Arctic, temperatures are rising even faster (interactive charts below and right). For 2010 and 2011, NASA recorded anomalies of over 2°C at higher latitudes (64N to 90N), with anomalies of over 3°C at latitudes 79N and 81N in 2010.

For November 2010, anomalies of 12.5°C were recorded at latitude 71N, longitude -79 (Baffin Island, Canada). At specific moments in time and at specific locations, anomalies can be even more striking. As an example, on January 6, 2011, temperature in Coral Harbour, located at the northwest corner of Hudson Bay in the province of Nunavut, Canada, was 30°C (54°F) above average.